Front End Of Line process (FEOL) operations are performed on the semiconductor wafer in the course of device manufacturing up to the first metallization. Back End Of Line process (BEOL) operation perform on the semiconductor wafer in the course of device manufacturing following the first metallization.
The present invention relates to the fabrication of semiconductor integrated circuits, and in particular, to the use of cleaning compositions comprising amidoxime compounds in the fabrication of semiconductor integrated circuits. Such cleaning compositions are useful in methods for cleaning plasma etch residue from semiconductor substrates and in methods for cleaning surfaces during fabrication, in particular, surfaces where the active components (transistors, resistors, etc.) are interconnected with wiring on the wafer—i.e., in the BEOL process.
BEOL generally begins when the first layer of metal is deposited on the wafer. It includes contacts, insulator, metal levels, and bonding sites for chip-to-package connections. Dicing the wafer into individual integrated circuit chips is also a BEOL process. More than 100 steps are involved in a standard integrated circuit (“IC”) manufacturing process that involves wafer cleaning or surface preparation. Wafer cleaning and surface preparation includes post-resist strip/ash residue removal, native oxide removal, and even selective etching. Although dry processes continue to evolve and offer unique advantages for some applications, most cleaning/surface preparation processes are “wet,” involving the use of a mixture of chemicals such as hydrofluoric; hydrochloric (HCl), sulfuric or phosphoric acid; or hydrogen peroxide, along with copious amounts of deionized water for dilution and rinsing. Wafers are typically processed in a batch immersion or batch spray system or, increasingly, with a single-wafer approach. The trend is toward more dilute chemistries, aided by the use of some form of mechanical energy, such as megasonics or jet-spray processing.
An important distinction in wafer cleaning today is that the main goal is not only particle removal, but some other function, such as removing oxide and photoresist residues after etching, stripping and/or ashing steps.
Surfaces may also be characterized as hydrophobic or hydrophilic. Hydrophilic surfaces in semiconductor substrates, include, for example, SiO2, carbon doped oxide (low k dielectric), copper oxide surfaces and benzotriazole treated copper surfaces. Hydrophobic surfaces are more difficult to clean, in part because cleaning solutions do not wet as well due to the high contact angle. During the drying step, the solutions tend to “bead” up on the surface, leaving particles on the surface instead of keeping the particles in solution. Hydrophobic surfaces are easily wetted by cleaning solutions, and, during drying, any particles on the surface tend to stay in solution until the solution is removed from the surface.
The analytical method for describing wetting and determining whether a surface is hydrophobic or hydrophilic is to measure contact angle.
Contact angle is a quantitative measure of the wetting of a solid by a liquid. It is defined geometrically as the angle formed by a liquid at the three phase boundary where a liquid, gas and solid intersect as shown below. Contact angle measurement characterizes the interfacial tension between a solid and a liquid drop. The technique provides a simple method to generate a great amount of information for surface analysis. And because the technique is extremely surface sensitive, it can be used in semiconductor cleaning applications. Contact angle measurement is a simplified method of characterizing the interfacial tension present between a solid, a liquid, and a vapor. As shown in FIG. 1, when a droplet of a high surface tension liquid rests on a solid of low surface energy, the liquid surface tension will cause the droplet to form a spherical shape (lowest energy shape). Conversely, when the solid surface energy exceeds the liquid surface tension, the droplet is a flatter, lower profile shape.
Most cleaning challenges are evolutionary as structures get smaller and specifications get tighter. The evolution is driven by a variety of new materials, new integration schemes and process flows.
Another common problem with cleaning semiconductor surfaces is the deposition of contaminants on the surface of the semiconductor device. Any cleaning solutions that deposit even a few molecules of undesirable composition, such as carbon or sodium, will adversely affect the performance of the semiconductor device. Cleaning solutions that require a rinsing step can also result in depositing contaminants on the surface. Thus, it is desirable to use a cleaning chemistry that is will leave little to no residue on the semiconductor surface.
It may also be desirable to have a surface wetting agent in the cleaning solution. Surface wetting agents prevent contamination of the semiconductor work-piece by helping to stop spotting of the surface caused by droplets clinging to the surface. Spotting (also called watermarks) on the surface can saturate metrology tools that measure light point defects, thus masking defects in the semiconductor work-piece.
In the manufacture of integrated circuits, interconnects are used to couple active and passive devices together and to couple together conductive lines formed on different layers of the integrated circuits. To keep the resistivity low, interconnects are generally fabricated from good conductors, such as gold, silver, aluminum, copper, or alloys of aluminum or copper. Keeping interconnects resistivity low will decreases the heat generated in the circuit, which permits the fabrication of higher density circuits. Unfortunately, even using conducting metals having a low resistivity, the interface between interconnects and an active or passive device or the interfaces between interconnect and a conductive line may have a high resistivity. High resistivity at an interconnect interface is often caused by an unclean surface at the interface.
More than one hundred steps are involved in a standard IC manufacturing process which involve wafer cleaning or surface preparation including post-resist strip/ash residue removal, native oxide removal, and even selective etching. Although dry processes continue to evolve and offer unique advantages for some applications, most cleaning/surface prep processes are “wet,” sometimes involving the use of other chemicals that may offer environmental challenges. Due to in part of environmental reasons, the use of more dilute chemistries has increased, aided by the use of some form of mechanical energy, such as megasonics or jet-spray processing. Accordingly, there is a need for chemistries that can effectively be used in diluted form.
Devices with critical dimensions on the order of 65 nanometers or less have involved integration of copper conductors and low-k dielectrics. Devices with critical dimensions on the order of 65 nanometers or less require alternating material deposition processes and planarization processes. Following almost each step in the fabrication process, e.g., a planarization step, a trenching step, or an etching step, cleaning processes are required to remove residues of the plasma etch, oxidizer, abrasive, metal or other liquids or particles remaining which contaminate the surface of the copper wafer. Fabrication of the current advanced generation of devices require copper conductors and low-k dielectric materials (typically carbon-silica or porous silica materials), both of which can react with and be damaged by various classes of prior art removers.
Low-k dielectrics in particular may be damaged in the cleaning process as evidenced by etching, changes in porosity/size, and ultimately changes in dielectric properties. Continuous wet process is required to remove the residues without any effect on damaged low-k layer, for instance k-value shift and CD loss. In addition, copper surface control is considered to be important for reliable electrical properties: Oxide layer on copper surface (CuOx) is required to be removed in the wet process and re-oxidation on the bare copper surface needs to be prevented.
In juxtaposition, cleaning needs and goals have become more demanding. Increasingly, wafers are being processed with a single-wafer approach, as compared to a batch immersion or batch spray system or, increasingly, with a single-wafer approach. This requires faster and effective chemical cleaning. Further, in wafer cleaning applications, particle removal may not be the main goal, but some other goal, such as removing native oxide or photoresist residue removal after strip/ash. Accordingly, there is a need for chemistries that can be used in both single-wafer and batch processing, while addressing a variety of goals in the removal process.
This concern in semiconductor cleaning processes increase the need to use chemistries containing more effective complexing agents.
Complexing agents for metal ions are required for a wide variety of industries. Examples of relevant purposes and uses are: detergents and cleaners, industrial cleaners, electroplating, water treatment and polymerizations, the photographic industry, the textile industry and the papermaking industry, and various applications in pharmaceuticals, in cosmetics, in foodstuffs and in plant feeding.
Most formulations being used in cleaning semiconductor substrates also contain complexing agents, sometimes called chelating agents.
Examples of complexing agents are nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), N,N′-bis(2-hydroxyphenyl)ethylenediiminodiacetic acid (HPED), triethylenetetranitrilohexaacetic acid (TTHA), desferriferrioxamin B,N,N′,N″-tris[2-(N-hydroxycarbonyl)ethyl]-1,3,5-benzenetricarboxamide (BAMTPH), and ethylenediaminediorthohydroxyphenylacetic acid (EDDHA), ethylenediaminetetramethylenephosphonic acid (EDTMP), propylenediaminetetraacetic acid (PDTA), hydroxypropylenediaminetetraacetic acid (HPDTA), isoserinediacetic acid (ISDA), β-alaninediacetic acid ({tilde over (β)}-ADA), hydroxyethanediphosphonic acid, diethylenetriaminetetraacetic acid, diethylenetriaminetetramethylenephosphonic acid, hydroxyethyleneaminodiacetic acid, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid and, furthermore, diethanolglycine, ethanolglycine, citric acid, glycolic acid, glyoxylic acid, lactic acid, phosphonic acid, glucoheptonic acid or tartaric acid, polyacrylates, carbonates, phosphonates, and gluconates.
In some cases, the biodegradability is also unsatisfactory. Thus, EDTA proves to have inadequate biodegradability in conventional tests, as does PDTA or HPDTA and corresponding aminomethylenephosphonates which, moreover, are often undesirable because of their phosphorus content. Phosphorus is also a dopant in semiconductor devices; therefore it is desirable to have cleaning solutions with non-phosphor containing compounds.
Much metal-chelating functionality is known. Metal chelation is when a central metal ion attaches by coordination links to two or more nonmetal atoms (ligands) in the same molecule. Heterocyclic rings are formed with the central (metal) atom as part of each ring. When the complex becomes more soluble in the solution, it functions as a cleaning process. If the complexed product is not soluble in the solution, it becomes a passivating agent by forming an insoluble film on top of the metal surface.
The current complexing agents being used as complexing agent for semiconductor cleaning include compounds, such as, glycolic acid, glyoxylic acid, lactic acid, phosphonic acid etc. They are acidic in nature and have a tendency to attack the residue and remove both metals and metal oxides, such as copper and copper oxide. This presents a problem for formulators where a chelating function is sought but only selectively to metal oxide and not the metal itself, e.g., in an application involving metal, such as copper. Accordingly, there is a need for complexing agents that are not aggressive toward metal substrates, while effectively providing for the chelation of metal ions residue created during the manufacturing processes.
The present invention addresses these problems.